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Cell : The Unit of Life

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
What is a centromere ? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

Centromere is a primary constriction present in the chromosome. It provides orientation to chromosome and marks the space for attachment of chromosomal fibres during cell division. The centromere has disc shaped structures called kinetochores on the sides of it.

Depending upon the location of centromere in a chromosome, the chromosome is classified  into the following four types :

(a) Telocentric: Centromere is present at the terminals.

(b) Acrocentric: Centromere is present near the terminals resulting in two short arms and two long arms.

(c) Sub- metacentric : Centromere divides the chromosomes into two unequal arms. It lies either below centre or above centre.

(d) Metacentric : Centromere divides the chromosomes into two equal arms with the centromere in the middle.

What is the function of contractile vacuole in amoeba?

Excretion.

Who concluded, “Cells are the ultimate units forming the structure of all plant tissues”?

Mathias Schleiden.

State one difference between gram positive and gram negative bacteria.

Gram positive bacteria retains the gram stain whereas the Gram negative bacteria does not.

Who reported that the cell had an outer layer which is known as plasma membrane today?

Theodore Schwann

What are receptor molecules ?

Receptor molecules are specific proteins in the cell's plasma membrane that receive chemical signals from outside the cell. When such chemical signals bind to a receptor, they cause some form of cellular response.

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